Process of recovering sulfurous acid.



No. s7a,|79. Patented July 9, I901.

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PROCESS OF RECOVEBING SULFUBOUS ACID.

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N0.v678,I79. Patented July 9, 19m. N. c. noosxms.

- PROCESS OF BECOVEBING SULFURDUS ACID.

(Application filed Apr. 28, 1900.; (No Model.) 3 Sheeis-Sheet 3.

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N ta STATES I FFICE.

TENT NELSON O. IIODGKINS, OF AUGUSTA, MAINE, ASSIGNOR OF ONE-HALF TO LEWIS H. SANFORD, OF SAME PLACE.

PROCESS OFRECOVERING SULFURQOUS ACID.

SPECIFICATION forming part Of Letters Patent N0. 678,179, dated July 9, 1901.

Application filed April 23, 1900. Serial No. 13,959- (No specimens.)

To all whom it may concern.-

Be it known that I, NELSON O. HODGKINS, a citizen of the United States, residing at Augusta, in the county of Kennebec and State of Maine, have invented a new and useful Process of Reclaiming Sulfurous Acid, of which the following is a specification.

My invention is an improved process of reclaiming sulfurous acid and sulfurous-acid gas blown off from a digester during the reduction of wood topulp by the sultite process, the object of my invention being to provide a novel process wherebya higher percentage of sulfurous acid can be saved from the ventings of the digester than formerly and whereby the gas maybe separated from the vented liquor of the lower grades and reclaimed.

In the accompanying drawings, Figure Us a vertical sectional view of a gas-separator for reclaiming the gas from the vented liquor embodying my improvements, the same being shown in operative relation to a digester. Fig. 2 is a diagrammatic elevation of a pulpdigesting apparatus provided with reclaiming apparatus embodying my improvements. Fig. 3 is a similar view of a modified form of the same.

' The apparatus shown in Figs. 1 and 2 of the drawings is particularly described and claimed in my pending application for Letters Patent of the United States, Serial No. 717,001, filedll/Iay 16, 1899.

The modified form of apparatus shown in Fig. 3 of the drawings is particularly described and claimed in an application for Letters Patent of the United States executed by me April 10, 1900, Serial No. 13,960, and filed simultaneously herewith.

In the digestion of wood and reduction of the same to pulp by my improved process the digesters A are filled with wood chips charged with sulfurous acid and heated by steam, the cooking process continuing about seven hours. It is necessary to entirelyfill the digesters with the chips and the cooking liquor or acid, so that the chips will be entirely submerged and those at the top of the digesters prevented from burning during the initial stages of the cooking. The chips which at first float eventually become entirely saturated with the digestive liquor and tend to sink, and

as the temperature of the digestive liquor is raised the expansion and pressure thereof in the digester is such as to render it necessary from time to time to partially vent the diges ter of some of the digestive liquor in order to relieve the digester of the excessive pressure.

The first venting occurs usually when the temperature of the digestive liquor has been raised to about 120 Fahrenheitqand theliquor discharged by the initial ventings is practically pure sulfurous acid, which is discharged in a solid volume from the digester. This venting is effected by openinga valve in the pipe 10, thereby permitting the vented liquor to pass into the separator 11, from which, the valve 16 being closed, the liquor passes through the pipe 17 to the drum 18, from the latter through the pipe 20 to a receiver, which may be eithera storage-tank O, as shown in Fig. 2, or a tank in the acid system, as

shown in Fig. 3. The pipe 20 has a coil located in a chamber B, in which a circulation of water is maintained through suitable pipes 22 24, such chamber B being a cooling-chamber, the office of which is to reduce the tem perature of the vented liquor after the same has been vented from the digester and before it reaches the receiver. In about two hours the temperature reaches about 250 Fahrenheit, after which the vented digestive liquor is no more than discolored water and sulfurous-acid gas, the lime having been taken up by the chips. During the cooking process, which continues, as before stated,about seven hours, the temperature is maintained from about 300 to 320 Fahrenheit. When the liquid vented from the digester assumes a reddish tinge, which may be ascertained by inspection of the glass gage on the separator, the valve 16 is opened and the red liquor permitted to be discharged from the separator through the pipe 12 into the tray 13, where it commingles with the water which circulates with the water in said trap through the vwater-pipes 14 15 and is discharged, The pressure in the separator being reduced and the temperature correspondinglylowered, a-partial separation of the gas from the red liquor is effected in the separator, and the temperature of the red liquor as it reaches the trap being further lowered the gas contained in the red liquor will not descend to the cold water in the trap, but separates from the red liquor, the liquor which is worthless escaping through the pipe 13 into a sewer or the like and the gas reclaimed therefrom rising in the pipe 12 into the separator, following the line of least resistance, and passing from the separator through the pipe 12, drum 1S, and coil 20 into the coil of the cooling-chamber B, where it is condensed by the reduction of temperature and passes into the receiver.

The receiver may be either a storage-tank (indicated at O) and connected with the third tank of the acid system used in the making of the sulfurous acid by the Well-known process, as shown in Fig. 2, or one of the said acid-tanks may be utilized as a receiver for the reclaimed acid and gas by connecting the pipe 20 directly with said tank, as at 25 in Fig. 3, in which event the lime-water in said acid-tank and in which the sulfurous-acid gas is forming is enriched by the addition thereto of the reclaimed sulfurous acid and gas.

In Fig. 3 of the drawings, 25, 26, and 27 are respectively the first, second, and third tanks in the acid system employed in the manufacture of sulfnrous acid with which to charge the digesters, said tanks being connected together by the pipes 28 or in any other suitable manner. A tank 29 for lime-water is connected with the first tank 25 by a valved pipe 30, and the third tank 27' is connected with the retort D, in which the sulfur is vaporized, by a pipe 31, which includes a coil 82 in a cooling-chamber 23. A pipe 34. connects the tank 27 with the storage-tank O, a suitable pump (indicated diagrammatically at 35) being provided to convey the liquor or acid from said tank 27 to the storage-tank C. 13 represents the usual vacuum-pump employed to draw the sulfur-fumes from the retort through the lime-water in the tanks of the acid system, and said tanks are provided with the usual valved pipes 36, by means of which the lime-water may be drawn from one tank into another. As herein shown, I connect the pipe 20 with the first tank 25 in the acid system, thereby causing the reclaimed acid or liquor to be added to the acid or liquor which is in process of formation. It will be understood that said pipe 20 may be connected with either of the tanks in the acid system.

In the method heretofore practiced of utilizing waste gases discharged from a digester in the process of making sulfite pulp the same have been forced in a hot state into a new charge of cooking liquor, at or near the bottom thereof. This process is not economical nor entirely efficient and differs from my process of reclaiming vented digestive acid and gas, in which I cool the vented acid and convey said reclaimed and cooled acid to a suitable receiver, either a tank in the acid system or a suitable storage-tank,before the same is reconveyed to the digester and used in another cooking charge. By the said improved method I am enabled to obtain much better results than have been heretofore possible and to save atleast twenty per cent. more of the vented digestive liquor or acid.

Having thus described my invention, I claim 1. The herein-described method of reclaiming sulfurous acid and gas blown oif from a digester during the cooking process, consisting in reducing the temperature and pressure of the liquor initially vented and collecting the same, and separating the gas from the liquor of the lower grades subsequently blown 01f by reducing the pressure and lowering the temperature thereof.

2. The herein-described method of reclaiming sulfurous acid and gas blown off from a digester during the cooking process, consistingin reducing the temperature and pressure of the liquor initially vented and collecting the same, separating the gas from the vented liquor of the lower grades subsequently blown off, by reducing the pressure and lowering the temperature thereof, and conveying said reclaimed gas to the body of the liquor previously reclaimed.

3. In the digestion of wood-pulp by the sulfite process, the herein-described method consisting in relieving the digester of excessive pressure by partially venting the same of the digestive liquor therein contained, from time to time, collecting and reclaiming the pure digestive liquor initially vented and reclaiming the sulfurous-acid gas from the impure digestive liquor subsequently vented, by separating said gas from said impure digestive liquor.

In testimony that I claim the foregoing as my own I have hereto affixed my signature in the presence of two witnesses.

NELSON C. I'IODGKINS.

Witnesses:

J. W. GARNER, MAY 0. GLADMOND. 

